20:2 MORPHOLOGY AND EVOLUTION
the Gorilla and Gibbon. In the Chimpanzee and it is double. In the former the heads rose from the back of the knee-joint; the proximal one is inserted into a vertical line on the back of the internal condyle of the tibia, and the distal one is inserted into the oblique popliteal line, the posterior border of the subcutaneous area, the internal condvle and a line curving round it. In the Orang one head arises within the capsule of the knee-joint.
The tibialis postieus arises from the lower part of the head and upper part of the shaft of the fibula, the upper half of the interosseous membrane and the upper half of the tibia. It is inserted in the Chimpanzee as in Man. In the other Apes it has-additional insertions. Thus it goes to the sheath of the peroneus longus in the Orang, to the peroneal sheath and plantar ligaments in the Gibbon, to the ectocuneiform in the Gorilla. Hepburn $3) describes it as going to the meso- and ectocuneiform bones in the Chimpanzee.
The flexor longus digitorum in the Chimpanzee arises from the popliteal line and its continuation downwards to about an inch from the internal malleolus, and from the septum between it and the tibialis postieus. The tendon passes behind the internal malleolus and under the annular ligament to the sole, where it is connected to the flexor longus hallucis, flexor brevis digitorum and accessorius. It divides into tendons for the four outer toes. These tendons vary considerably in different individuals, there being differences in the degree to which they are connected to the flexor longus hallucis and flexor brevis digitorum. The tendons are inserted as in Man. In the same animal the flexor longus